Method and device for transmitting information using varying carrier frequencies by means of a frequency hopping method

ABSTRACT

A method and an apparatus transmits information in various carrier frequencies with frequency hopping. A table  25  with a plurality of n possible carrier frequency values fx in addresses  1  through N of the table  25  is thereby offered. Further, a sequence of random values is generated, for example in a random number generator  22 , on the basis whereof a part M of the N carrier frequency values fx is read from the corresponding addresses of the table  25 , whereby M≦N applies. Information is subsequently transmitted in the corresponding carrier frequencies. The inventive apparatus or, respectively, the inventive method can be implemented, for example, in a mobile station and/or a base station of a mobile radiotelephone system.

PRIORITY

The present application is a national stage entry under 35 U.S.C.,Section 371 of International Application PCT/DE98/01681 filed Jun. 18,1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method and to an apparatus forthe transmission of information in various carrier frequencies with afrequency hopping method that can be implemented, for example, in amobile station and/or a base station of a mobile radiotelephone system.

2. Description of the Related Art

What is referred to as the frequency hopping spread spectrum system isknown as a method for the transmission of data. What is thereby to beunderstood by a frequency hopping spread spectrum system is a systemwherein a plurality of carrier frequencies are offered for the radiotransmission of data, and the carrier frequency currently which isemployed is changed at periodic intervals. Particularly given atime-division multiplex system (TDMA), a change of the carrier frequencycan ensue after every time slot of the time frame of the time-divisionmultiplex transmission. Such a frequency hopping spread spectrum systemhas advantages to the effect that the energy of the entire radiotransmission is distributed over all carrier frequencies. This isparticularly advantageous when a generally available frequency band suchas, for example, the 2.4 GHz ISM (industrial, scientific, medical) bandis employed. According to the applicable regulations (FCC part 15 in theUSA), an upper limit for the maximally occurring energy per carrierfrequency is defined for this frequency band in order to keepinterference with other subscribers as low as possible. It is.prescribed for the frequency change that at least 75 differentfrequencies must be used within a time span of 30 seconds. Further, eachfrequency may be used for a maximum of 0.4 seconds in 30 seconds. Allfrequencies must be used equally distributed on time average.

24 time slots, respectively 12 for uplink and for downlink, are definedin a 10 ms frame in the Digital Enhanced Cordless Telecommunications(DECT) standard. The FCC part 15, however, only makes a bandwidth ofless than 1 MHz available in the ISM band. In order to meet thisrequirement, the plurality of time slots was reduced to 12 time slots ina 10 ms time frame, i.e. respectively 6 time slots for uplink and fordownlink.

With 6 time slots for each direction and retaining the DECT time frameof 10 ms, each time slot would exhibit a length of 833 μs. The time sslots in the DECT standard have a length of 417 μs. Given a slowfrequency hopping system, an inactive DECT time slot of 417 μs isrequired between two neighboring, active time slots wherein data istransmitted. In such systems, only 6 active time slots are respectivelyemployed for data transmission in each direction. If such systems thatwork on the basis of a slow frequency hopping are also to meet therequirements of the FCC part 15 in the ISM band, an inactive blind timeslot of 417 μs must in turn be present between neighboring active timeslots. This blind time slot thus has half the length of a full time slotof 833 μs, as a result whereof—when a base time frame of 10 ms isretained—four active time slots are offered in each frame for therespective uplink and downlink, a blind time slot being respectivelytransmitted between them. The four active time slots have a respectivelength of 833 μs, whereas the blind time slots comprises a respectivelength of 417 μs. Given this structure, the frequency programming forthe frequency hopping in the next, following active time slot cancontinue to be implemented at the end of the preceding active time slot.The programmed start frequency in the next active time slot can therebybe set during the blind time slots.

an advantage of the frequency hopping spread spectrum system is that thesystem becomes more insensitive to disturbances due to the offering of agreat plurality of carrier frequencies. Over and above this, thesecurity against tapping by third parties is enhanced in the system,since the third party generally does not know the carrier frequency towhich a switch is made after a certain time span.

The sequence of carrier frequencies that are successively employed forthe transmission is determined by an algorithm. Such an algorithm isidentically implemented in the fixed station as well as in each mobilestation of the mobile radiotelephone transmission. When, thus, a mobilepart is synchronized with the appertaining fixed station, the mobilepart and the fixed station undertakes the carrier frequency changepredetermined by the sequence of the algorithm synchronously with oneanother.

Problems occur when the plurality of usable carrier frequencies is nottemporally constant. This, for example, is the case when a carrierfrequency recognized as disturbed is blocked during a certain time spanand, thus, is not enabled for employment and, for example, is enabledfor re-employment after a certain time span. Even given such a pluralityof carrier frequencies fluctuating over time, it must be assured that,for example, the aforementioned FCC part 15 rules are adhered to.

European Patent Document EP-A-0 182 762 discloses a method in atelecommunication system having two transmission/reception stations thatselects carrier frequencies according to the frequency hopping method,whereby new carrier frequencies are selected from a matrix withavailable frequencies by generating a sequence of random numbers thatreference the position of a respective carrier frequency in the matrixand on the basis of status information for the respective frequencylikewise stored in the matrix, so that they can be read out in a nextstep.

U.S. Pat. No. 5,471,503 discloses a method for sampling a receptionsignal in a telecommunication working according to the frequency hoppingmethod, whereby each channel checks for an existing transmission.

SUMMARY OF THE INVENTION

An object of the present invention is to create a method and anapparatus for the transmission of information in various carrierfrequencies with a frequency hopping method wherein a simple andeffective offering of the carrier frequencies is assured.

This object is achieved by a method and an apparatus for thetransmission of information in various carrier frequencies with afrequency hopping method the method including the following steps:offering a table with a plurality of n possible carrier frequency valuefx in addresses 1 through N of the table; generating a sequence ofrandom values; reading out at least a part M of the N carrier frequencyvalues fx from the corresponding addresses of the table on the basis ofthe generated sequence of random values, whereby M≦N; and transmittinginformation in the corresponding carrier frequencies, whereby thefollowing steps are implemented for the setup of a connection: samplinga carrier frequency; deciding whether a message containing at least aninitialization information was received on this carrier frequency duringa specific time span; when the decision is negative, selecting a newcarrier frequency and sampling this new carrier frequency; when thedecision is positive, generating the sequence of random values uponemployment of the initialization information. The apparatus includes ameans for offering a table with a plurality of n possible carrierfrequency value fx in addresses 1 through N of the table; a means forgenerating a sequence of random values; a means for reading out at leasta part M of the N carrier frequency values fx from the correspondingaddresses of the table on the basis of the generated sequence of randomvalues, whereby M≦N; and a means for transmitting information in thecorresponding carrier frequencies, whereby a means for the setup of aconnection is provided that comprises: means for sampling a carrierfrequency; means for deciding whether a message containing at least aninitialization information was received on this carrier frequency duringa specific time span; configured such that, when the decision isnegative, a new carrier frequency is selected and this new carrierfrequency is sampled, and, when the decision is positive, the sequenceof random values is generated upon employment of at least theinitialization information. Advantageous developments of the presentinvention are provided in that the generated sequence of random valuesis converted into address values between 1 and N with which the carrierfrequency values are read from the table. The following steps areimplemented for the synchronization: sampling a carrier frequency;deciding whether a message was received on this carrier frequency duringa specific time span; when the decision is negative, selecting a newcarrier frequency and sampling this new carrier frequency; when thedecision is positive, generating the sequence of random values uponemployment of the message. In a preferred embodiment, a part M of the Npossible carrier frequency values is read out from the table, wherebythe remaining N-M carrier frequency values are employed for replacingdisturbed carrier frequency values of the M carrier frequency values.Specifically, the table is updated from the N-M carrier frequency valuesbefore the read-out upon replacement of the carrier frequency valuesthat correspond to disturbed carrier frequencies.

In the preferred apparatus, a means for converting the generatedsequence of random values into address values between 1 and N with whichthe carrier frequency values are read from the table. A means forsynchronization is provided that comprises: means for sampling a carrierfrequency; means for deciding whether a message containing at least aninitialization information was received on this carrier frequency duringa specific time span, configured such that, when the decision isnegative, a new carrier frequency is selected and this new carrierfrequency is sampled, and, when the decision is positive, the sequenceof random values is generated upon employment of at least theinitialization information. The apparatus includes the means for readoutreads a part M of the N possible carrier frequency values from thetable, whereby the remaining N-M carrier frequency values are employedfor replacing disturbed carrier frequency values of the M carrierfrequency values. A means for updating that updates the table from theN-M carrier frequency values before the readout upon replacement of thecarrier frequency values that correspond to disturbed carrierfrequencies.

According to the invention, a table having a plurality of M possiblecarrier frequency values fx is offered in addresses 1 through N of thetable. Further, a sequence of random values is generated on whose basisat least a part M of the N carrier frequency fx is read out from thecorresponding addresses of the table, whereby M≦N applies. Subsequently,information are transmitted in the carrier frequencies corresponding tothe carrier frequency values. The inventive apparatus can, for example,be a mobile station or a base station as well of a mobile radiotelephone system.

The generated sequence of random values is converted into address valuesbetween 1 and N with which the carrier frequency values fx are read fromthe table.

Advantageously, one carrier frequency is sampled first for setting up aconnection, for example between mobile radio telephone units. Then adecision is made as to whether a specific message was received on thiscarrier frequency during a specific time span. When the decision isnegative, a new carrier frequency is selected and this new carrierfrequency is sampled. When the decision is positive, the table isinitialized and the sequence of random values is generated uponemployment of the received, specific message. This is advantageousparticularly in a mobile station of a mobile radio telephone system towhich a specific message is communicated from a base station, thismaking it possible for the mobile station to begin the sequence ofrandom values for reading out the carrier frequency values at theaddress at which the mobile station is likewise located at the moment.Since the same sequence of random values is generated in the mobilestation and the base station, the same sequence of carrier frequencyvalues is thus subsequently read out from the table. The same method isemployed for synchronizing, for example, mobile radio telephone unitssince, for example, a mobile station likewise thereby requires a messagefrom the base station on whose basis it can continue to read carrierfrequency values from the table at the same location of the randomsequence.

Advantageously, only one part M of the possible carrier frequency valuesis read out from the table, whereby the remaining N-M carrier frequencyvalues are employed for replacing disturbed carrier frequency values ofthe M carrier frequency values.

When setting up a connection, for example between mobile radio telephoneunits, or when synchronizing, for example, mobile radio telephone units,can thereby be updated before the readout upon replacement of thecarrier frequency values that correspond to the disturbed carrierfrequencies from the N-M carrier frequency values. In the case of amobile station, for example, this can receive a message regarding whichcarrier frequencies are disturbed from a base station wherein thedisturbed carrier frequencies were acquired. On the basis of thismessage, the disturbed carrier frequency values are then updated bynon-disturbed carrier frequency values from the N-M carrier frequencyvalues. The table is updated in the same way as well as in thecorresponding base station. It is to be emphasized again that the basestation and the mobile station respectively.

The aforementioned method steps are implemented in corresponding devicesin the inventive apparatus. The inventive apparatus for the transmissionof information in various carrier frequencies with a frequency hoppingmethod can thereby be implemented, for example, in a mobile station orin a base station of a mobile radio telephone system.

DESCRIPTION OF THE DRAWINGS

The invention is now explained in greater detail on the basis of anexemplary embodiment and with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a mobile radio telephone transmissionsystem with an inventive fixed station;

FIG. 2 is a graph in perspective view of a time frame of a datatransmission standard as employable given the present invention;

FIG. 3 is a functional block diagram showing details of the internalstructure of an inventive base station;

FIG. 4 is a graph in perspective view of a frequency hopping spreadspectrum system, particularly for the case of a jammer-evasion mode aswell;

FIG. 5 shows a table from which carrier frequency values are randomlyread on the basis of a random sequence;

FIG. 6 shows a flow chart that shows a method for setting up aconnection between or, respectively, for the synchronization of twomobile radial telephone units;

FIG. 7 shows a table from which only a part of the carrier frequencyvalues is read out randomly on the basis of a random sequence;

FIG. 8 shows a flow chart that illustrates a method for setting up aconnection between or, respectively, for the synchronization of, forexample, two mobile radio telephone units, whereby disturbed carrierfrequency values can be replaced by non-disturbed carrier frequencyvalues;

FIG. 9 shows a table from which only a part of the carrier frequencyvalues are randomly read out on the basis of a random sequence;

FIG. 10 shows the table from FIG. 9, whereby a disturbed carrierfrequency value from the carrier frequency values that are read out isreplaced by a non-disturbed carrier frequency value; and

FIG. 11 shows the table of FIG. 10, whereby another disturbed carrierfrequency value is replaced by a non-disturbed carrier frequency value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 1, the general structure of a mobile radiotelephone transmission shall be explained first. As generally standard,the arrangement for radio transmission of data comprises a fixed station1 and a plurality of mobile parts (mobile stations), cordless telephones2, 3 . . . The fixed station 1 is connected to the fixed network with aterminal line 10. An interface means (not shown) can be provided forcommunication between the fixed station and the terminal line 10. Thefixed station 1 comprises an antenna 6 with which, for example, acommunication with the mobile part 2 occurs via a first radiotransmission path 8 or with the mobile part 3 via a second radiotransmission path 9. The mobile parts 2, 3 . . . comprise a respectiveantenna 7 for the reception or, respectively, the transmission of data.In FIG. 1, the condition is schematically shown wherein the fixedstation 1 actively communicates with the mobile part 2 and thusexchanges data therewith. The mobile part 3, in contrast, is in what isreferred to as the idle locked mode wherein, standby-like, it waits fora call from the fixed Station 1. In this condition, the mobile part 3does not communicate with the fixed station 1 in the actual sense butreceives the data of, for example, a time slot from the fixed station 1at periodic intervals in order to be able to resynchronize its carrierfrequencies fx.

The internal structure of the fixed station 1 is schematically shown inFIG. 1. The voice information data are supplied to a RF module 4 that isdriven by a carrier frequency sequence unit. The exact structure of aninventive fixed station 1 shall be described later.

With reference to FIG. 2, a transmission standard shall now be explainedof a type that can be employed given the present invention. As can beseen from FIG. 2, data are transmitted on a plurality of carrierfrequency fx¹-10 thereof being shown—in chronological succession in aplurality of time slots, 24 time slots Zx in the illustrated case, beingtransmitted in a time-division multiplex method in TDMA (time divisionmultiple access). In the illustrated case, work is thereby carried outin a duplex mode, i.e. following the transmission of the first 12 timeslots Zx, a switch is made to reception and the twelve time slots (Z13through Z24) are received from the fixed station in the oppositedirection.

When what is referred to as the DECT standard is employed for thetransmission, the time duration of a time frame amounts to 10 ms and 24time slots Zx are provided, namely 12 time slots for the transmissionfrom the fixed station to mobile parts and another 12 time slots Zx forthe transmission from the mobile parts to the fixed station. Accordingto the DECT standard, ten carrier frequencies fx are provided between1.88 GHz and 1.90 GHz.

Of course, other frame structures are also suitable for employment inthe present invention, for example those wherein the number of timeslots per frame is cut in half compared to the DECT standard.

The present invention is particularly employed for transmissions in whatis referred to as the 2.4 GHz-ISM (Industrial, Scientific, Medical)frequency band. The generally accessible ISM frequency band comprises abandwidth of 83.5 MHz. According to the rule FCC part 15, at least 75carrier frequencies must be distributed over these 83.5 MHz. A divisionof the bandwidth of 83.5 MHz onto 96 carrier frequencies is especiallyadvantageous, i.e. a channel spacing of 864 kHz. The aforementionedfrequency bands and standards are cited merely as examples. Afundamental precondition for an applicability in the present inventionis merely that what is referred to is a frequency hopping spreadspectrum is employed, i.e. that a plurality of carrier frequencies areavailable and that the carrier frequency selected for the transmissionis changed from time to time. A precondition for such a change is thatthe data are transmitted in time slots Zx (time-division multiplexmethod). Thus, for example, the DECT standard is suitable, as is anyother modified standard based on this DECT standard.

With reference to FIG. 3, the internal structure of an inventive fixedstation 1 shall now be explained in greater detail. As can be seen inFIG. 3, information data are supplied to the RF module 4 whentransmission is to be carried out from the fixed station 1 to a mobilepart 2, 3 . . . with the antenna 6, and the RF module 4 outputsinformation data when data when data are received from mobile parts. TheRF module 4 modulates the digitally encoded information data onto acarrier frequency fx. The carrier frequency fx to be currently employedis thereby prescribed by a carrier frequency sequence unit, which isreferenced 20 overall. An acquisition means 24 to which the demodulatedsignal is supplied from the RF module 4 is provided in the carrierfrequency sequence unit 20. Disturbance thereby means that either adisturbance in the actual sense or an occupancy by some othertransmitter is present. A disturbance in the sense the presentspecification can thus be acquired in that a received signal isdemodulated on a carrier frequency and acquired as to whether a signallevel is present on this carrier frequency or not. A disturbed carrierfrequency is thus a carrier frequency onto which a signal is modulatedthat exceeds a specific threshold.

Alternatively to the blocking, the A-CRC value, the X-CRC value, a lossof synchronization or the RSSI value can be utilized.

On the basis of the demodulated signal from the RF module 4, forexample, the acquisition means 24 thus determines how high the signalpart modulated onto a specific carrier frequency fx is. When theacquired signal part lies above a predetermined limit value, theacquisition means 24 outputs a disturbance acquired signal to aninhibit/enable unit 21. Dependent on the disturbance acquisition signalfrom the acquisition means 24, the inhibit/enable unit 21 forwards aninhibit/enable information to a processor 23. This inhibit/enableinformation indicates which of the carrier frequencies fx are inhibitedor, respectively, re-enabled due to the acquisition of a disturbance bythe acquisition means 24, as shall be explained later.

The acquisition means 24 and the inhibit/enable means 21 thus creates andependent procedure with which disturbed frequencies can be inhibitedand re-enabled. In addition to being supplied with the inhibit/enableinformation from the inhibit/enable unit 21, the processor 23 issupplied with a sequence from a random generator 22. On the basis of animplied random algorithm, the random generator 22 generates a randomlydistributed sequence of carrier frequency values within the useablefrequency band. The random generator 22 thus implements a procedureindependent of the procedure of frequency blocking for the case of adisturbance. The processor 23, finally, outputs a drive signal to the RFmodule 4 that prescribes the carrier frequency value to be employed forthe RF 15 module 4.

The processor 23 comprises a table 25′ provided in a memory whosefunction and administration shall be explained later.

With reference to FIG. 4, the operation of a fixed station 1 or,respectively, the method shall be explained in greater detail. As shownin FIG. 4, for example, a carrier frequency f1 is employed during aframe Rx of a mobile radio transmission, as shown shaded in FIG. 4. Thisfrequency f1 is thus the first value of the sequence generated by therandom generator 22 that is supplied to the processor 23, which in turncorrespondingly drives the RF module 4. Let it be assumed for the frameR2 that the random generator 22 prescribes a frequency hop P1 onto acarrier frequency f3 on the basis of its calculated frequency.

Let the case now be assumed that the acquisition means 24, for examplein a prior transmission, has acquired that the carrier frequency f2 isdisturbed, and the acquisition means 24 has thus forwarded acorresponding disturbance signal to the inhibit/enable unit 21 that inturn indicates an inhibit of the frequency f2 to the processor 23. Letit also be assumed that the random generator 22 prescribes the carrierfrequency f2 previously acquired as disturbed on the basis of itsidentified sequence for the frame R3. Proceeding from the coincidence ofthe prescribed carrier frequency f2 according to the sequence of therandom generator 22 and, simultaneously, the inhibit signal from theinhibit/enable unit 21 for the same carrier frequency f2, the processor23 now replaces the carrier frequency f2 that was actually prescribedbut was acquired as disturbed for the frame R3 by a carrier frequencythat was not acquired as disturbed by the acquisition means 24, forexample the carrier frequency f4, as indicated by the frequency hoparrow P3. Instead of the carrier frequency 2 actually prescribed by thesequence, thus, the RF module 4 is driven onto the alternate carrierfrequency f4. By replacing the carrier frequency acquired as disturbed,thus, a modified sequence of carrier frequencies is created. Themodified sequence thereby comprises only undisturbed carrierfrequencies. As a result thereof that a carrier frequency acquired asdisturbed is replaced and not skipped, the positions of the undisturbedcarrier frequencies in the modified sequence upon transition to thefollowing carrier frequency is not modified compared to the originalsequence.

The basis of this modified sequence composed of only undisturbed carrierfrequency fx is thus formed by two superimposed, mutually independentprocedures (random generator 22 or, respectively, inhibit/enable unit21). This inhibit can be in turn canceled by the inhibit/enable unit 21as soon as a renewed acquisition by the acquisition means 24 indicatesthat the previously disturbed carrier frequency is now no longerdisturbed. In this case, the inhibit/enable unit 21 provides an enablesignal to the processors 23 that indicates that the processor 23 now nolonger need replace the previously disturbed carrier frequency by adifferent carrier frequency.

Alternatively, the inhibit/enable unit 21 can automatically output anenable signal to the processor 23 without renewed acquisition by theacquisition means 24 as soon as a predetermined time duration hasexpired. Each of said procedures thus independently assures that theentire, predetermined frequency spectrum is utilized and uniformlydistributed. Standards are thus adhered to by the adaptation of thetimes in the procedure for inhibiting frequencies.

Let the U.S. rule FCC part 15 be cited as an example of such a standard.This rule prescribes that at least 75 different frequencies must be usedgiven a frequency hopping spread spectrum system within a time span ofthirty seconds. Each frequency is thereby allowed to be used for amaximum of 0.4 seconds in 30 seconds. Over and above this, allfrequencies must be used equally distributed on average.

The fixed station 1 is the master in the frequency allocation, i.e. therandom generator in a mobile part is initialized at the beginning of aconnection setup with the status of the random number generator 22 ofthe fixed station 1. Subsequently, the random number generators in amobile part 2, 3 . . . and in the fixed station 1 generate the samecarrier frequency values synchronously in the frame clock andautonomously from one another.

The mobile part comprises essentially the same structure as the fixedstation 1. Like the fixed station 1, the mobile part likewise comprisesa carrier frequency sequence unit 20 with a random number generator 22and a processor 23 that contains a table 25. The table 25 is identicalto the table 25 of the fixed station 1. The mobile station, however,does not comprise the acquisition means 24 and the inhibit/enable means21. Disturbed carrier frequencies are thus only acquired in the fixedstation or, respectively, base station and communicated to thecorresponding mobile stations. An acquisition of disturbed carrierfrequencies can also occur in the mobile stations, whereby the mobilestations comprise the structure shown in FIG. 3 in this case. The methodfor transmitting information or, respectively, data in the correspondingcarrier frequencies in the mobile stations corresponds to thecorresponding method in the base station.

The procedure for frequency blocking that is implemented by theacquisition means 24 and the inhibit/enable unit 21 employs aunidirectional protocol on the air interface during the entireconnection time between the fixed station 1 and a mobile part 2, 3 . . .When the acquisition means 24 finds one of the ultimately possiblefrequencies fx of the fixed station 1 to be disturbed, then the fixedstation 1 thus informs all mobile parts with which it is maintaining anactive connection that this disturbed frequency—when it is generated bythe frequency of the random number generator—is to be replaced byanother carrier frequency acquired as being not disturbed. The frequencyinhibit is in turn canceled by the inhibit /enable unit 21 when theinhibited carrier frequency is again suitable for the transmission or,respectively, when it was inhibited for longer than a previously definedtime.

It can be seen in FIG. 3 that, for example, a table 25 provided in amemory is allocated to the processor 23. With reference to FIG. 3 aswell as to FIG. 5 through FIG. 11, it shall now be explained how thecarrier frequencies fx are inventively offered. As can be seen in FIG.5, all carrier frequencies fx available overall are entered into a table25, for example 96 carrier frequencies fx.

As can be seen in FIG. 5, the carrier frequency values f₁ through f₆ areentered in corresponding addresses 1 through 96 of the table 25 in theirnumerical sequence. This sequence of the carrier frequency values fx,however, is only envisioned as an example. The carrier frequency valuesfx can, for example, be stored in the table 25 in a different sequence.

The number of carrier frequency values fx present overall, 96 in thepresent example, is referenced N. According to U.S. rule FCC part 15, atleast 75 different frequencies must be used in a time span of 30seconds.

It is assumed in the example explained in FIGS. 5 and 6 that no carrierfrequency is disturbed, so that all 96 carrier frequencies can beemployed for the transmission of data. Given the example explained inFIGS. 7 and 8, only a part M of the 96 carrier frequencies, namely 75carrier frequencies, are transmitted; these, when one of them isdisturbed, can be replaced from the remaining 21 carrier frequencies.

The table 25 permanently stored in the table 25′ in the mobile stationand in the base station or, respectively, fixed station is read out witha random number generator 22 that is identical for the base station andthe fixed station. The carrier frequency values fx read out in theprocessor 23, which is likewise respectively present in the base stationand in the mobile station, are converted into the corresponding carrierfrequencies in the RF module 4. Subsequently, data or, respectively,information are transmitted in the carrier frequencies. Each carrierfrequency value fx is present only a single time in the table 25.

FIG. 6 shows a flow chart that shows the setup of a connection between amobile station and a base station or, respectively, the synchronizationof a mobile station to a base station. The executive sequences areidentical in both instances. The method execution shown in FIG. 6 is, inparticular, implemented in the mobile stations that are dependent on therespective base station. A corresponding means in the respective mobileradial telephone unit that, for example, can be a mobile station isallocated to each of the method steps shown in FIG. 6. In a first step26, a selected carrier frequency is sampled in a corresponding means. Ina next step 27, a determination or, respectively, decision is made in acorresponding means as to whether a specific message was received on theselected carrier frequency. The specific message can thereby, forexample, be a N_(t) message in the A-field of the DECT standard. Other,corresponding messages can be employed in other standards. When it isfound in step 27 that the specific message was not received, a check iscarried out in a step 28 in a corresponding means as to whether aspecific time duration t has elapsed. When the specific time duration thas not elapsed, then the sampling of the selected carrier frequency iscontinued in step 26. When the time duration t has elapsed, then a newcarrier frequency is selected in a step 29 in a corresponding means. Thenew carrier frequency is correspondingly sampled in the step 26.

When the decision in step 27 is positive, i.e. when it is found that thespecific, anticipated message was received on the carrier frequency, therandom number sequence permanently prescribed by the random numbergenerator 22 is generated in a corresponding means in a step 30. Thespecific, received message is thereby employed to start the generationof the random number sequence in the random number generator 22 at theposition at which the mobile unit from which the specific message wasreceived is located at the moment. This is necessary in order to assurethat the two, data-exchanging mobile radio telephone units aresynchronized with one another and employ the random sequence of carrierfrequencies for the transmission of data synchronously with one another.In step 30, thus, the random number sequence is generated beginning withthe position prescribed by the specific message and is employed for thereadout of carrier frequency values proceeding from the correspondingaddress in the table 25. The readout of carrier frequency values fxensues in a step 31 in a corresponding means in the processor 23 of thecorresponding mobile radio telephone u nit. The random number valuesthat are generated by the random number generator 22 are therebyconverted into address values between 1 and N, i.e. into address valuesbetween 1 and 96 in the present example, with which the carrierfrequency values fx are read out from the table 25.

FIG. 7 shows a table 25 wherein only a part M=75 of the total of N=96carrier frequency values fx are read out from corresponding addresses 1through 75. As was already explained above, for example, at least 75different frequencies must be used in a time span of 30 secondsaccording to U.S. rule FCC part 15. This requirement is satisfied by thereadout of the first 75 carrier frequency values from the correspondingaddresses 1 through 75 from the table 25 according to FIG. 7. Theremaining carrier frequency values from the addresses 76 through 96 canthereby be employed for replacing or, respectively, updating disturbedcarrier frequency values in the first 75 carrier frequency values. Therandom number generator 22 in the mobile station and the base stationtherefore outputs no sequences that comprise N different values; on thecontrary, it is adequate when it outputs M different valuescorresponding to the carrier frequencies actually available. As wasexplained with reference to FIG. 3, for example, one or more disturbedcarrier frequencies are thereby identified in a fixed station. Inresponse thereto, the fixed station outputs a corresponding signal tothe mobile station regarding which frequencies are disturbed. Thecarrier frequency values in the table 25 in the base station and themobile station that correspond to disturbed carrier frequencies aresubsequently replaced by non-disturbed carrier frequency values from theaddresses 76 through 96. Of course, this replacement and updating of thedisturbed carrier frequency values must ensue synchronously in the basestation and in the mobile station. Further, the identification ofdisturbed carrier frequencies could also ensue in the respective mobilestation that sends a corresponding message to allocated base stations.

FIG. 8 shows a flow chart that explains the setup of a connectionbetween mobile radio telephone units or, respectively, thesynchronization of mobile radio telephone units when only a part M ofthe existing N carrier frequency values is read out from the table 25.The corresponding method steps of the flow chart of FIG. 5 havecorresponding devices in the respective mobile radio telephone unitallocated to them.

In a first step 26, a selected carrier frequency is sampled in acorresponding means. In a step 27, a decision is made in a correspondingmeans as to whether a specific message was received on the selectedcarrier frequency. When this is not the case, a finding is made in astep 28 as to whether a time duration t has elapsed. The step 27 and thestep 28 can be implemented in a common step in a common means. When itis found that the time duration t has not elapsed, then the selectedcarrier frequency is re-sampled in the step 26. When it is found thatthe time duration t has elapsed, then a new carrier frequency isselected in a step 29 in a corresponding means and is correspondinglysampled in the step 26.

When the decision in the step 27 is positive, i.e. when it is found thata specific message is received on the sampled carrier frequency, thenthe random sequence is generated by the random number generator 22 uponemployment of the received message. The specific message can thereby,for example, be the N_(t) message in the A-field in the DECT standard.In other standards, of course, other messages can be employed. Thespecific message thereby informs the random number generator 22regarding the position proceeding from which the random sequence shouldbe started. In other words, the specific message indicates the positionat which the random number generator 22 of that mobile radio telephoneunit that sends the specific message is located at the moment, so thatthe random number generator 22 of the receiving mobile radio telephoneunit to be synchronized can generate the random sequence proceeding fromthe same position.

In a step 32, the table is updated in a corresponding means on the basisof a further, received message. When, for example, the base stationfinds that a specific carrier frequency is disturbed, then itcommunicates a message to, for example, a receiving mobile station as towhich carrier frequency is disturbed and with which carrier frequencyfrom the addresses 76 through 96 of the table 25 the disturbed carrierfrequency value should be replaced. In a step 31, the carrierfrequencies are read out from the addresses 1 through 75 of the table 25in a corresponding means.

FIGS. 9 through 11 show how disturbed carrier frequency values in theaddresses 1 through 75 of the table 25 are replaced by non-disturbedcarrier frequency values from the addresses 76 through 96. FIG. 9thereby shows a table 25 that corresponds to the table 25 of FIG. 7. Apart M, for example 75, of carrier frequency values fx is read out fromcorresponding addresses 1 through M on the basis of the random numbersequence generated by the random number generator 22. When it is foundthat, for example, the carrier frequency that corresponds to the carrierfrequency value f₃ is disturbed, then the carrier frequency values f₉₆,which is not disturbed, is substituted for the carrier frequency valuef₃, as shown in FIG. 10. The non-disturbed carrier frequency value f₉₆is thus located at the address 3, and the disturbed carrier frequencyvalue f₃ is located at the address 96. Since the addresses 1 through 75are always read out on the basis of the random sequence, it is thusassured that only non-disturbed carrier frequencies are employed for thetransmission of data. When it is also found that the carrier frequencythat corresponds to the carrier frequency value f₇₅ is disturbed andthat the carrier frequency value f₃ is no longer disturbed, then thecarrier frequency value f₃ is first reset to its original address 3, andthe carrier frequency value f₉₆ is reset to its original address 96.Subsequently, the disturbed carrier frequency value f₇₅ is set to theaddress 96, and the non-disturbed carrier frequency f₉₆ is set to theaddress 75, as shown in FIG. 11. Since the table is permanentlyprescribed, it is thus assured that the carrier frequency values arealways present at their fixed addresses except when they are disturbed.

The values N=96 and M=75 are merely exemplary in the above descriptionand can be replaced by other values dependent on the requirements of thestandard to be met.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

1. A method for transmission of information in various carrierfrequencies with frequency hopping, comprising the following steps:offering a table with a plurality of n possible carrier frequency valuefx in addresses 1 through N of the table; generating a sequence ofrandom values; reading out at least a part M of the N carrier frequencyvalues fx from corresponding addresses of the table on a basis of thegenerated sequence of random values, M≦N, and transmitting informationin the corresponding carrier frequencies, implementing the followingsteps for setup of a connection: sampling a carrier frequency; decidingwhether a message containing at least an initialization information wasreceived on this carrier frequency during a specific time span; when thedeciding step is negative, selecting a new carrier frequency andsampling said new carrier frequency; and when the deciding step ispositive, generating the sequence of random values upon employment ofthe initialization information.
 2. The method according to claim 1,further comprising the step of converting, the generated sequence ofrandom values into address values between 1 and N with which the carrierfrequency values are read from the table.
 3. The method according toclaim 1, comprising the following steps: implementing a synchronizationincluding the steps of sampling a carrier frequency; deciding whether amessage was received on said carrier frequency during a specific timespan; when the deciding step is negative, selecting a new carrierfrequency and sampling said new carrier frequency; when the decidingstep is positive, generating the sequence of random values uponemployment of the message.
 4. The method according to claim 1, furthercomprising the steps of reading out a part M of the N possible carrierfrequency values from the table, employing remaining N-M carrierfrequency values for replacing disturbed carrier frequency values of theM carrier frequency values.
 5. The method according to claim 4, furthercomprising the step of updating from the N-M carrier frequency valuesbefore the read-out upon replacement of the carrier frequency valuesthat correspond to disturbed carrier frequencies.
 6. An apparatus fortransmission of information in various carrier frequencies with afrequency hopping method, comprising: a table with a plurality of npossible carrier frequency value fx in addresses 1 through N of thetable; a random value generator for generating a sequence of randomvalues; a means for reading out at least a part M of the N carrierfrequency values fx from corresponding addresses of the table on a basisof the generated sequence of random values, M≦N; a transmittingapparatus for transmitting information in the corresponding carrierfrequencies, a means for setup of a connection that includes: means forsampling a carrier frequency; and means for deciding whether a messagecontaining at least an initialization information was received on saidcarrier frequency during a specific time span configured such that, whenthe decision is negative, a new carrier frequency is selected and saidnew carrier frequency is sampled, and, when the decision is positive,the sequence of random values is generated upon employment of at leastthe initialization information.
 7. The apparatus according to claim 6,further comprising: a means for converting the generated sequence ofrandom values into address values between 1 and N with which the carrierfrequency values are read from the table.
 8. The apparatus according toclaim 6, further comprising a means for synchronization including: meansfor sampling a carrier frequency; means for deciding whether a messagecontaining at least an initialization information was received on saidcarrier frequency during a specific time span configured such that, whenthe decision is negative, a new carrier frequency is selected and saidnew carrier frequency is sampled, and, when the decision is positive,the sequence of random values is generated upon employment of at leastthe initialization information.
 9. The apparatus according to claim 6,wherein the means for readout reads a part M of the N possible carrierfrequency values from the table, the remaining N-M carrier frequencyvalues being employed for replacing disturbed carrier frequency valuesof the M carrier frequency values.
 10. The apparatus according to claim9, further comprising a means for updating the table from the N-Mcarrier frequency values before the read-out upon replacement of thecarrier frequency values that correspond to disturbed carrierfrequencies.